As a UI/UX agency that focusses on B2B SaaS, I’ve always found Fantasy UIs fascinating. It’s the complete opposite of the simple & clean interfaces clients ask us to design. I’ve spent some time thinking about why these Fantasy UIs are so fascinating despite the fact they seem not very user friendly. My conclusion was that fantasy Interfaces are very much like the early web. Lots of moving parts (dancing banana gifs)…
Complex-tight layouts will feel cluttered to people who have more difficulty with differentiation, visually processing contrast - or aren't motivated/driven/interested to understand what they're looking at. If you can expect the audience who needs to learn the interface will be motivated to learn it, then it can work.
I've had similar desire to see higher quality, more complex "fantasy" UIs and I could see parts of projects benefitting from such an interface - however I'm a long way off from having the funding and experimental budget to move in that direction. Maybe I'll be blessed enough that it can happen in 5 years.